Frame equipped membrane electrode assembly, method of producing the frame equipped membrane electrode assembly, and fuel cell

ABSTRACT

A frame equipped membrane electrode assembly includes a membrane electrode assembly and a frame member having a first frame shaped sheet provided on an outer peripheral portion of the membrane electrode assembly over the entire periphery. An outer peripheral portion of an electrolyte membrane is provided between a cathode and the first frame shaped sheet, stacked on an outer peripheral portion of the cathode, and joined to an inner peripheral portion of the first frame shaped sheet through an adhesive layer. The adhesive layer is filled in an area surrounded by an inner peripheral end of the first frame shaped sheet, an anode, and the electrolyte membrane.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a frame equipped membrane electrode assembly, a method of producing the frame equipped membrane electrode assembly, and a fuel cell.

Description of the Related Art

In general, a solid polymer electrolyte fuel cell employs a solid polymer electrolyte membrane. The solid polymer electrolyte membrane is a polymer ion exchange membrane. The fuel cell includes a membrane electrode assembly (MEA) formed by providing an anode on one surface of the solid polymer electrolyte membrane, and a cathode on the other surface of the solid polymer electrolyte membrane.

The membrane electrode assembly is sandwiched between separators (bipolar plates) to form a power generation cell unit cell). In use, a predetermined number of power generation cells are stacked together to form an in-vehicle fuel cell stack, for example.

In recent years, in an attempt to reduce the quantity of the relatively expensive solid polymer electrolyte membrane, and protect the thin solid polymer electrolyte membrane having the low strength, a frame equipped MEA including a resin frame member in its outer periphery has been adopted. In the frame equipped MEA disclosed in U.S. Pat. No. 8,399,150, an inner peripheral portion of the resin frame member is joined to an outer peripheral portion of the electrolyte membrane.

SUMMARY OF THE INVENTION

In the technique of U.S. Pat. No. 8,399,150, if the electrolyte membrane is exposed at a gap formed in a joint part where the MEA and the resin frame member are joined together, the electrolyte membrane is not positioned fixedly. Therefore, there is a concern that, in the event that expansion or contraction of the electrolyte membrane occurs when the electrolyte membrane is humidified or dried, the electrolyte membrane may be damaged undesirably.

The present invention has been made taking such a problem into account, and an object of the present invention is to provide a frame equipped membrane electrode assembly, a method of producing the frame equipped membrane electrode assembly, and a fuel cell in which it is possible to reduce damage of an electrolyte membrane even if expansion or contraction of the electrolyte membrane occurs when the electrolyte membrane is humidified or dried.

In order to achieve the above object, according to a first aspect of the present invention, a frame equipped membrane electrode assembly is provided. The frame equipped membrane electrode assembly includes a membrane electrode assembly and a frame member including a resin sheet, the membrane electrode assembly includes an electrolyte membrane, a first electrode provided on one surface of the electrolyte membrane, and a second electrode provided on another surface of the electrolyte membrane, and the frame member including a resin sheet provided on an outer peripheral portion of the membrane electrode assembly over its entire periphery, wherein an outer peripheral portion of the electrolyte membrane is disposed between the second electrode and the resin sheet, stacked on an outer peripheral portion of the second electrode, and joined to an inner peripheral portion of the resin sheet through an adhesive layer, and the adhesive layer is filled in an area surrounded by an inner peripheral end of the resin sheet, the first electrode, and the electrolyte membrane.

According to a second aspect of the present invention, a fuel cell is provided. The fuel cell includes a frame equipped membrane electrode assembly and separators provided on both sides of the frame equipped membrane electrode assembly, respectively, the frame equipped membrane electrode assembly including a membrane electrode assembly and a frame member, the membrane electrode assembly including an electrolyte membrane, a first electrode provided on one surface of the electrolyte membrane, and a second electrode provided on another surface of the electrolyte membrane, the frame member including a resin sheet provided on an outer peripheral portion of the membrane electrode assembly over its entire periphery, wherein an outer peripheral portion of the electrolyte membrane is disposed between the second electrode and the resin sheet, stacked on an outer peripheral portion of the second electrode, and joined to an inner peripheral portion of the resin sheet through an adhesive layer, and the adhesive layer is filled in an area surrounded by an inner peripheral end of the resin sheet, the first electrode, and the electrolyte membrane.

According to a third aspect of the present invention, a method of producing a frame equipped membrane electrode assembly is provided. The frame equipped membrane electrode assembly includes a membrane electrode assembly and a frame member, the frame equipped membrane electrode assembly including an electrolyte membrane, a first electrode provided on one surface of the electrolyte membrane, and a second electrode provided on another surface of the electrolyte membrane, and the frame member including a resin sheet provided on an outer peripheral portion of the membrane electrode assembly over its entire periphery. The method includes the steps of disposing the electrolyte membrane, the first electrode, the second electrode, and the resin sheet in a manner that an inner peripheral portion of the resin sheet is disposed between an outer peripheral portion of the first electrode and an outer peripheral portion of the second electrode and that the adhesive layer provided on at least the inner peripheral portion of the resin sheet is overlapped with the electrolyte membrane, and thermal compression bonding to join the electrolyte membrane, the first electrode, the second electrode, and the resin sheet by thermal compression bonding in a manner that the outer peripheral portion of the electrolyte membrane is stacked on the outer peripheral portion of the second electrode, and joined to the inner peripheral portion of the resin sheet through the adhesive layer, wherein in the thermal compression bonding step, a part of the adhesive layer is allowed to flow from a position between the resin sheet and the electrolyte membrane to an area surrounded by an inner peripheral end of the resin sheet, the first electrode, and the electrolyte membrane and to be filled in the area.

In the present invention, the adhesive layer which joins the inner peripheral portion of the resin sheet and the outer peripheral portion of the electrolyte membrane is filled in the area surrounded by the inner peripheral end of the resin sheet, the first electrode, and the electrolyte membrane. In the structure, it is possible to prevent exposure of the electrolyte membrane in the area. Therefore, even if expansion or contraction of the electrolyte membrane occurs when the electrolyte membrane is humidified or dried, it is possible to reduce damage of the electrolyte membrane.

The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view showing main components of a power generation cell (fuel cell) according to an embodiment of the present invention;

FIG. 2 is a cross sectional view taken along a line II-II in FIG. 1;

FIG. 3A is a perspective view showing a frame member;

FIG. 3B is a view showing a MEA joining step;

FIG. 3C is a perspective view showing an obtained frame equipped membrane electrode assembly;

FIG. 4A is a view showing a step of providing the frame member between an anode and a cathode; and

FIG. 4B is a view showing a step of thermal compression bonding.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIGS. 1 and 2, a power generation cell (fuel cell) 12 includes a frame equipped membrane electrode assembly 10 (hereinafter referred to as the “frame equipped MEA 10”), and a first separator 14 and a second separator 16 provided on both sides of the frame equipped MEA 10. For example, the power generation cell 12 is a laterally elongated (longitudinally elongated) rectangular solid polymer electrolyte fuel cell. A plurality of power generation cells 12 are stacked together in a horizontal direction indicated by an arrow A or in a gravity direction indicated by an arrow C to form a fuel cell stack 11 a. For example, the fuel cell stack 11 a is mounted in a fuel cell electric automobile (not shown) as an in-vehicle fuel cell stack.

In the power generation cell 12, the frame equipped MEA 10 is sandwiched between the first separator 14 and the second separator 16. Each of the first separator 14 and the second separator 16 has a laterally elongated (or longitudinally elongated) rectangular shape. For example, the first separator 14 and the second separator 16 are steel plates, stainless steel plates, aluminum plates, plated steel sheets, or metal plates having anti-corrosive surfaces by surface treatment. Alternatively, carbon member or the like may be used as the first separator 14 and the second separator 16.

The rectangular frame equipped MEA 10 includes a membrane electrode assembly 10 a (hereinafter referred to as the “MEA 10 a”). The MEA 10 a includes an electrolyte membrane 18, an anode (first electrode) 20 provided on one surface of the electrolyte membrane 18, and a cathode (second electrode) 22 provided on the other surface of the electrolyte membrane 18.

For example, the electrolyte membrane 18 includes a solid polymer electrolyte membrane (cation ion exchange membrane). For example, the solid polymer electrolyte membrane is a thin membrane of perfluorosulfonic acid containing water. The electrolyte membrane 18 is interposed between the anode 20 and the cathode 22. A fluorine based electrolyte may be used as the electrolyte membrane 18. Alternatively, an HC (hydrocarbon) based electrolyte may be used as the electrolyte membrane 18.

The surface size (outer size) of the anode 20 is larger than the surface sizes of the electrolyte membrane 18 and the cathode 22. Therefore, the outer peripheral end of the anode 20 is positioned outside an outer peripheral end 18 e of the electrolyte membrane 18 and an outer peripheral end 22 e of the cathode 22 over the entire periphery. It should be noted that, instead of adopting the above structure, the surface size of the anode 20 may be smaller than the surface sizes of the electrolyte membrane 18 and the cathode 22.

As shown in FIG. 2, the anode 20 includes a first electrode catalyst layer 20 a joined to one surface 18 a of the electrolyte membrane 18, and a first gas diffusion layer 20 b stacked on the first electrode catalyst layer 20 a. The surface sizes of the first electrode catalyst layer 20 a and the first gas diffusion layer 20 b are the same, and larger than the surface sizes of the electrolyte membrane 18 and the cathode 22.

The surface size of the cathode 22 is smaller than the surface size of the anode 20. The outer peripheral end 22 e of the cathode 22 and the outer peripheral end 18 e of the electrolyte membrane 18 are positioned inside an outer peripheral end 20 e of the anode 20 over the entire periphery.

It should be noted that the surface size of the cathode 22 may be larger than the surface size of the anode 20, and the outer peripheral end 22 e of the cathode 22 may be positioned outside the outer peripheral end 20 e of the anode 20 over the entire periphery.

The cathode 22 includes a second electrode catalyst layer 22 a joined to a surface 18 b of the electrolyte membrane 18, and a second gas diffusion layer 22 b stacked on the second electrode catalyst layer 22 a. The surface sizes of the second electrode catalyst layer 22 a, the second gas diffusion layer 22 b, and the electrolyte membrane 18 are the same. Therefore, as viewed in the thickness direction (indicated by the arrow A) of the MEA 10 a, the outer peripheral end 22 e of the cathode 22 and the outer peripheral end 18 e of the electrolyte membrane 18 are provided at the same position over the entire periphery.

For example, the first electrode catalyst layer 20 a is formed by porous carbon particles deposited uniformly on the surface of the first gas diffusion layer 20 b together with an ion conductive polymer binder and platinum alloy supported on the surfaces of the porous carbon particles. For example, the second electrode catalyst layer 22 a is formed by porous carbon particles deposited uniformly on the surface of the second gas diffusion layer 22 b together with an ion conductive polymer binder and platinum alloy supported on the surfaces of the porous carbon particles.

Each of the first gas diffusion layer 20 b and the second gas diffusion layer 22 b comprises a carbon paper or a carbon cloth, etc. The surface size of the second gas diffusion layer 22 b is smaller than the surface size of the first gas diffusion layer 20 b. The first electrode catalyst layer 20 a and the second electrode catalyst layer 22 a are formed on both surfaces of each electrolyte membrane 18.

The frame equipped MEA 10 further includes a rectangular frame member 24 which is provided along the outer periphery of the electrolyte membrane 18 over the entire periphery, and joined to the anode 20 and the cathode 22. The frame member 24 includes two frame shaped sheets (resin sheet). Specifically, the frame member 24 includes a first frame shaped sheet 24 a having an inner peripheral portion 24 an joined to an outer peripheral portion of the MEA 10 a, and a second frame shaped sheet 24 b joined to the first frame shaped sheet 24 a.

The first frame shaped sheet 24 a and the second frame shaped sheet 24 b are directly joined together by an adhesive layer 24 c of an adhesive 24 d over the entire periphery (over the entire periphery of the surface of the second frame shaped sheet 24 b adjacent to the first frame shaped sheet 24 a). The second frame shaped sheet 24 b is joined to the outer peripheral portion of the first frame shaped sheet 24 a. The thickness of an outer peripheral portion 24 g of the frame member 24 is larger than the thickness of the inner peripheral portion of the frame member 24 (inner peripheral portion 24 an of the first frame shaped sheet 24 a).

The first frame shaped sheet 24 a and the second frame shaped sheet 24 b are made of resin material. Examples of materials of the first frame shaped sheet 24 a and the second frame shaped sheet 24 b include PPS (polyphenylene sulfide), PPA (polyphthalamide), PEN (polyethylene naphthalate), PES (polyethersulfone), LCP (liquid crystal polymer), PVDF (polyvinylidene fluoride), a silicone resin, a fluororesin, m-PPE (modified polyphenylene ether) resin, PET (polyethylene terephthalate), PBT (polybutylene terephthalate), or modified polyolefin.

The inner peripheral portion 24 an of the first frame shaped sheet 24 a is positioned between an outer peripheral portion 20 c of the anode 20 and an outer peripheral portion 22 c of the cathode 22. Specifically, the inner peripheral portion 24 an of the first frame shaped sheet 24 a is held between an outer peripheral portion 18 c of the electrolyte membrane 18 and the outer peripheral portion 20 c of the anode 20. The inner peripheral portion 24 an of the first frame shaped sheet 24 a and the outer peripheral portion 18 c of the electrolyte membrane 18 are joined together through the adhesive layer 24 c. In the structure, the outer peripheral portion 18 c of the electrolyte membrane 18 is positioned between the cathode 22 and the first frame shaped sheet 24 a, stacked on the outer peripheral portion 22 c of the cathode 22, and joined to the inner peripheral portion of the first frame shaped sheet 24 a through the adhesive layer 24 c. In the embodiment of the present invention, the adhesive layer 24 c is provided continuously from the inner peripheral portion to the outer peripheral portion of the first frame shaped sheet 24 a. The adhesive layer 24 c for joining the first frame shaped sheet 24 a and the second frame shaped sheet 24 b and the adhesive layer 24 c for joining the inner peripheral portion of the first frame shaped sheet 24 a and the outer peripheral portion 18 c of the electrolyte membrane 18 may be provided independently (separately) from each other.

The inner peripheral portion 24 an of the first frame shaped sheet 24 a includes an overlap part 24 ak overlapped with the outer peripheral portion 20 c of the anode 20 over the entire periphery as viewed in the thickness direction of the MEA 10 a. The inner peripheral portion 24 an of the first frame shaped sheet 24 a may be interposed between the electrolyte membrane 18 and the cathode 22 in the state where the adhesive layer 24 c is joined to the surface 18 b of the electrolyte membrane 18.

A step is provided in the anode 20 at a position corresponding to an inner peripheral end 24 ae of the first frame shaped sheet 24 a. Specifically, the anode 20 has an inclined area 21 c inclined from the electrolyte membrane 18, between an area 21 a overlapped with the inner peripheral portion 24 an of the first frame shaped sheet 24 a and an area 21 b overlapped with the electrolyte membrane 18.

On the other hand, the cathode 22 has a flat shape from an area 23 a overlapped with the inner peripheral portion 24 an of the first frame shaped sheet 24 a to an area 23 b overlapped with the electrolyte membrane 18. Instead of adopting the above structure, the cathode 22 may have an inclined area inclined from the electrolyte membrane 18 (area inclined in a direction opposite to the inclined area 21 c), between the area 23 a overlapped with the inner peripheral portion 24 an of the first frame shaped sheet 24 a and the area 23 b overlapped with the electrolyte membrane 18. The anode 20 may have the inclined area 21 c and the cathode 22 may have the inclined area.

It should be noted that, instead of adopting the above structure, the anode 20 may have a flat shape from the area 21 a overlapped with the inner peripheral portion 24 an of the first frame shaped sheet 24 a to the area 21 b overlapped with the electrolyte membrane 18, and the cathode 22 may have an inclined area inclined from the electrolyte membrane 18, between the area 23 a overlapped with the inner peripheral portion 24 an of the first frame shaped sheet 24 a and the area 23 b overlapped with the electrolyte membrane 18.

The second frame shaped sheet 24 b is joined to the outer peripheral portion of the first frame shaped sheet 24 a. The thickness of the first frame shaped sheet 24 a and thickness of the second frame shaped sheet 24 b may be the same or may be different from each other.

An inner peripheral end 24 be of the second frame shaped sheet 24 b is positioned outside the inner peripheral end 24 ae of the first frame shaped sheet 24 a (in a direction away from the MEA 10 a) over the entire periphery. A gap G is formed between the inner peripheral end 24 be of the second frame shaped sheet 24 b and the outer peripheral end 22 e of the cathode 22 over the entire periphery.

The inner peripheral end 24 be of the second frame shaped sheet 24 b is positioned inside the outer peripheral end 20 e of the anode 20 over the entire periphery. As viewed in the thickness direction (indicated by an arrow A) of the MEA 10 a, the inner peripheral portion of the second frame shaped sheet 24 b includes an overlap part 24 bk overlapped with the outer peripheral portion 20 c of the anode 20 over the entire periphery. The inner peripheral end 24 be of the second frame shaped sheet 24 b is positioned outside the outer peripheral end 18 e of the electrolyte membrane 18.

The adhesive layer 24 c is provided over an entire surface 24 as of the first frame shaped sheet 24 a adjacent to the second frame shaped sheet 24 b (adjacent to the cathode 22). The adhesive layer 24 c joins the inner peripheral portion 24 an of the first frame shaped sheet 24 a and the outer peripheral portion 18 c of the electrolyte membrane 18. At the position of the above gap G, the first frame shaped sheet 24 a is exposed to the gap G through the adhesive layer 24 c.

The adhesive layer 24 c is filled in an area R surrounded by the inner peripheral end 24 ae of the first frame shaped sheet 24 a, the anode 20, and the electrolyte membrane 18. In the cross section taken along the thickness direction of the MEA 10 a, the area R has a triangular shape. Hereinafter, a part of the adhesive layer 24 c filled in the area R will be referred to as a filling part 24 cf. In the step of producing the MEA 10 a (the step of joining the components of the MEA 10 a by thermal compression bonding), the adhesive layer 24 c (adhesive 24 d) between the first frame shaped sheet 24 a and the electrolyte membrane 18 is softened (liquefied) by heat, flows into the area R, and hardened (solidified) in the area R to form the filling part 24 cf.

In the area R, the filling part 24 cf is fixed (adhered) to the electrolyte membrane 18. In the area R, the filling part 24 cf is fixed to the inner peripheral end 24 ae of the first frame shaped sheet 24 a, and the surface of the anode 20 (first gas diffusion layer 20 b) adjacent to the cathode 22 as well. As viewed in the thickness direction of the MEA 10 a, each of the area R and the filling part 24 cf has a rectangular shape formed along the inner peripheral end 24 ae of the first frame shaped sheet 24 a, and extends along the inner peripheral end 24 ae over the entire periphery.

The thickness t1 of the adhesive layer 24 c (filling part 24 cf) filled in the area R is larger than the thickness t2 of the adhesive layer 24 c between the first frame shaped sheet 24 a and the electrolyte membrane 18. The thickness t2 of the adhesive layer 24 c between the first frame shaped sheet 24 a and the electrolyte membrane 18 is smaller than the thickness t3 of the adhesive layer 24 c between the outer peripheral end 22 e of the cathode 22 and the inner peripheral end 24 be of the second frame shaped sheet 24 b.

As the adhesive 24 d of the adhesive layer 24 c, for example, liquid adhesive or a hot melt sheet is provided. The adhesive 24 d is not limited to a liquid or solid adhesive, and not limited to a thermoplastic or thermosetting adhesive, etc. The adhesive 24 d chiefly contains thermoplastic material. The adhesive 24 d may be an adhesive which contains thermoplastic material in some part of the adhesive. Examples of the adhesive 24 d include an acrylic based adhesive. Alternatively, the adhesive 24 d may be a rubber-based, urethane based, ester based, or ethylene vinyl based adhesive.

An overlap part K where the anode 20, the first frame shaped sheet 24 a, and the cathode 22 are overlapped with each other is held between a ridge 39 of the first separator 14 protruding toward the anode 20 and a ridge 37 of the second separator 16 protruding toward the cathode 22.

The elastic modulus E1 of the first frame shaped sheet 24 a, the elastic modulus E2 of the adhesive layer 24 c, and the elastic modulus E3 of the electrolyte membrane 18 are determined to satisfy the following magnitude relationship. The “elastic modulus” herein all means “tensional elastic modulus”. The elastic modulus E1 of the first frame shaped sheet 24 a is larger than the elastic modulus E3 of the electrolyte membrane 18. The elastic modulus E2 of the adhesive layer 24 c is smaller than the elastic modulus E1 of the first frame shaped sheet 24 a and the elastic modulus E3 of the electrolyte membrane 18. That is, the elastic modulus E1 of the first frame shaped sheet 24 a, the elastic modulus E2 of the adhesive layer 24 c, and the elastic modulus E3 of the electrolyte membrane 18 are determined to satisfy the relationship of: E1>E3>E2.

The elastic modulus E2 of the adhesive layer 24 c is determined to be, e.g., not more than 50% of the elastic modulus E3 of the electrolyte membrane 18. The elastic modulus E2 of the adhesive layer 24 c is determined to be, e.g., not more than 30% of the elastic modulus E3 of the electrolyte membrane 18. The elastic modulus E2 of the adhesive layer 24 c is determined to be, e.g., not more than 20% of the elastic modulus E3 of the electrolyte membrane 18. The elastic modulus E2 of the adhesive layer 24 c is determined to be, e.g., not more than 10% of the elastic modulus E3 of the electrolyte membrane 18. The elastic modulus E2 of the adhesive layer 24 c is determined to be, e.g., not more than 5% of the elastic modulus E3 of the electrolyte membrane 18.

The elastic modulus E1 of the first frame shaped sheet 24 a at 120° C. is, e.g., not less than 1000 Mpa. The elastic modulus E2 of the adhesive layer 24 c at 120° C. is, e.g., not more than 0.5 Mpa. In the case where the elastic modulus E2 of the adhesive layer 24 c is too low (e.g., not more than 0.1 Mpa), cushioning effects cannot be realized. The elastic modulus E3 of the electrolyte membrane 18 at 120° C. is, e.g., in the range between 10 Mpa and 100 Mpa.

The thickness of the electrolyte membrane 18 and the thickness of the adhesive layer 24 c are smaller than the thickness of the first frame shaped sheet 24 a. The thickness of the electrolyte membrane 18 and the thickness of the adhesive layer 24 c are determined to become relatively close to each other. The thickness of the first frame shaped sheet 24 a is, e.g., in the range between 25 μm and 150 μm. The thickness of the adhesive layer 24 c is, e.g., in the range between 10 μm and 50 μm. The thickness of the electrolyte membrane 18 is, e.g., in the range between 6 μm and 20 μm.

As shown in FIG. 1, at one end of the power generation cell 12 in the direction indicated by the arrow B (in the horizontal direction), an oxygen-containing gas supply passage 30 a, a coolant supply passage 32 a, and a fuel gas discharge passage 34 b are provided. The oxygen-containing gas supply passage 30 a, the coolant supply passage 32 a, and the fuel gas discharge passage 34 b extend through the power generation cell 12 in the direction indicated by the arrow A. An oxygen-containing gas is supplied through the oxygen-containing gas supply passage 30 a, and a coolant is supplied through the coolant supply passage 32 a. A fuel gas such as a hydrogen-containing gas is discharged through the fuel gas discharge passage 34 b. The oxygen-containing gas supply passage 30 a, the coolant supply passage 32 a, and the fuel gas discharge passage 34 b are arranged in the vertical direction indicated by the arrow C.

At the other end of the power generation cell 12 in the direction indicated by the arrow B, a fuel gas supply passage 34 a for supplying the fuel gas, a coolant discharge passage 32 b for discharging the coolant, and an oxygen-containing gas discharge passage 30 b for discharging the oxygen-containing gas are provided. The fuel gas supply passage 34 a, the coolant discharge passage 32 b, and the oxygen-containing gas discharge passage 30 b extend through the power generation cell 12 in the direction indicated by the arrow A. The fuel gas supply passage 34 a, the coolant discharge passage 32 b, and the oxygen-containing gas discharge passage 30 b are arranged in the direction indicated by the arrow C.

The first separator 14 has a fuel gas flow field 38 on its surface 14 a facing the frame equipped MEA 10. The fuel gas flow field 38 is connected to the fuel gas supply passage 34 a and the fuel gas discharge passage 34 b. Specifically, the fuel gas flow field 38 is formed between the first separator 14 and the frame equipped MEA 10. The fuel gas flow field 38 includes a plurality of straight flow grooves (or wavy flow grooves) extending in the direction indicated by the arrow B.

The second separator 16 has an oxygen-containing gas flow field 36 on its surface 16 a facing the frame equipped MEA 10. The oxygen-containing gas flow field 36 is connected to the oxygen-containing gas supply passage 30 a and the oxygen-containing gas discharge passage 30 b. Specifically, the oxygen-containing gas flow field 36 is formed between the second separator 16 and the frame equipped MEA 10. The oxygen-containing gas flow field 36 includes a plurality of straight flow grooves (or wavy flow grooves) extending in the direction indicated by the arrow B.

A coolant flow field 40 is formed between a surface 14 b of the first separator 14 and a surface 16 b of the second separator 16 that are adjacent to each other. The coolant flow field 40 is connected to the coolant supply passage 32 a and the coolant discharge passage 32 b, and extends in the direction indicated by the arrow B.

As shown in FIG. 2, a plurality of ridges 39 forming the fuel gas flow field 38 are provided on the surface 14 a of the first separator 14 (facing the frame equipped MEA 10). The ridges 39 are expanded toward the anode 20, and contact the anode 20. A plurality of ridges 37 forming the oxygen-containing gas flow field 36 are provided on the surface 16 a of the second separator 16 (facing the frame equipped MEA 10). The ridges 37 are expanded toward the cathode 22, and contact the cathode 22. The MEA 10 a is held between the ridges 37, 39.

One or a plurality of bead seals 42 are formed on the surface 14 a of the first separator 14, around the outer peripheral portion of the first separator 14, for preventing leakage of the fuel gas to the outside. The bead seals 42 are formed by press forming, and are expanded toward the frame member 24. The inner bead seal 42 is provided around the fuel gas flow field 38, the fuel gas supply passage 34 a, and the fuel gas discharge passage 34 b while allowing the fuel gas flow field 38 to be connected to the fuel gas supply passage 34 a and the fuel gas discharge passage 34 b.

Resin material 43 (or rubber material) is fixed to protruding front end surfaces of the bead seals 42 by printing, coating, etc. The bead seals 42 contact the first frame shaped sheet 24 a (area overlapped with the second frame shaped sheet 24 b) through the resin material 43 in an air tight and liquid tight manner. The resin material 43 may be fixed to the first frame shaped sheet 24 a.

Instead of the bead seals 42, solid seals made of elastic material protruding toward the frame member 24 may be provided on the first separator 14.

One or a plurality of bead seals 44 are formed on the surface 16 a of the second separator 16, around the outer peripheral portion of the second separator 16, for preventing leakage of the oxygen-containing gas to the outside. The bead seals 44 are formed by press forming, and are expanded toward the frame member 24. The inner bead seal 44 is provided around the oxygen-containing gas flow field 36, an oxygen-containing gas supply passage 30 a, and an oxygen-containing gas discharge passage 30 b while allowing the oxygen-containing gas flow field 36 to be connected to the oxygen-containing gas supply passage 30 a and the oxygen-containing gas discharge passage 30 b.

Resin material 45 (or rubber material) is fixed to protruding front end surfaces of the bead seals 44 by printing, coating, etc. The bead seals 44 contact the second frame shaped sheet 24 b (area overlapped with the first frame shaped sheet 24 a) through the resin material 45 in an air tight and liquid tight manner. The resin material 45 may be fixed to the second frame shaped sheet 24 b.

Instead of the bead seals 44, solid seals made of elastic material protruding toward the frame member 24 may be provided on the second separator 16.

Examples of the resin materials 43, 45 include polyester fiber, silicone, EPDM, FKM, etc. The resin materials 43, 45 are not essential. The resin materials 43, 45 may be dispensed with (in this case, the bead seal 42 contacts the first frame shaped sheet 24 a directly, and the bead seal 44 contacts the second frame shaped sheet 24 b directly).

The bead seal 42 and the bead seal 44 face each other through the frame member 24. The outer peripheral portion of the frame member 24 (area where the first frame shaped sheet 24 a and the second frame shaped sheet 24 b are overlapped with each other) is held between the bead seal 42 of the first separator 14 and the bead seal 44 of the second separator 16. In the case where the above solid seals are provided on the first separator 14 and the second separator 16, the outer peripheral portion of the frame member 24 (the area where the first frame shaped sheet 24 a and the second frame shaped sheet 24 b are overlapped with each other) is held between the solid seal of the first separator 14 and the solid seal of the second separator 16.

Operation of the fuel cell stack 11 a including the power generation cell 12 having the above structure will be described below.

As shown in FIG. 1, an oxygen-containing gas is supplied to the oxygen-containing gas supply passage 30 a, and a fuel gas such as a hydrogen-containing gas is supplied to the fuel gas supply passage 34 a. Further, a coolant such as pure water, ethylene glycol, or oil is supplied to the coolant supply passage 32 a.

Thus, the oxygen-containing gas flows from the oxygen-containing gas supply passage 30 a into the oxygen-containing gas flow field 36 of the second separator 16. The oxygen-containing gas flows in the direction indicated by the arrow B, and the oxygen-containing gas is supplied to the cathode 22 of the MEA 10 a. In the meanwhile, the fuel gas flows from the fuel gas supply passage 34 a into the fuel gas flow field 38 of the first separator 14. The fuel gas flows along the fuel gas flow field 38 in the direction indicated by the arrow B, and the fuel gas is supplied to the anode 20 of the MEA 10 a.

Thus, in the MEA 10 a, the oxygen-containing gas supplied to the cathode 22 and the fuel gas supplied to the anode 20 are partially consumed in the electrochemical reactions in the second electrode catalyst layer 22 a and the first electrode catalyst layer 20 a to generate electricity.

Then, in FIG. 1, the oxygen-containing gas supplied to the cathode 22 is partially consumed at the cathode 22, and discharged along the oxygen-containing gas discharge passage 30 b in the direction indicated by the arrow A. Likewise, the fuel gas supplied to the anode 20 is partially consumed at the anode 20, and the fuel gas is discharged along the fuel gas discharge passage 34 b in the direction indicated by the arrow A.

Further, the coolant supplied to the coolant supply passage 32 a flows into the coolant flow field 40 between the first separator 14 and the second separator 16, and then, flows in the direction indicated by the arrow B. After the coolant cools the MEA 10 a, the coolant is discharged from the coolant discharge passage 32 b.

Next, an example of a method of producing the frame equipped MEA 10 will be described.

As shown in FIG. 3A, the above frame member 24 is provided (produced) by joining the first frame shaped sheet 24 a and the second frame shaped sheet 24 b together by the adhesive layer 24 c. An opening 53 is formed at the center of the first frame shaped sheet 24 a, inside the inner peripheral end 24 be of the second frame shaped sheet 24 b. The fuel gas supply passage 34 a, the fuel gas discharge passage 34 b, the oxygen-containing gas supply passage 30 a, the oxygen-containing gas discharge passage 30 b, the coolant supply passage 32 a, and the coolant discharge passage 32 b are formed in the frame member 24.

Next, an MEA joining step is performed as shown in FIG. 3B. In the MEA joining step, the gap G (see FIG. 2) is formed between the inner peripheral end 24 be of the second frame shaped sheet 24 b and the outer peripheral end 22 e of the cathode 22 (which has been joined to the electrolyte membrane 18). In this state, the inner peripheral portion 24 an of the first frame shaped sheet 24 a is provided between the outer peripheral portion 20 c of the anode 20 and the outer peripheral portion 22 c of the cathode 22, for joining the first frame shaped sheet 24 a to the anode 20 and the cathode 22. In this case, the heat and load are applied to the anode 20, the first frame shaped sheet 24 a, the electrolyte membrane 18, and the cathode 22 stacked together in the thickness direction (hot pressing is performed) to join these components together (by thermal compression bonding). As a result, as shown in FIG. 3C, the frame member 24 is joined to the outer peripheral portion of the MEA 10 a, and the frame equipped MEA 10 is obtained.

Specifically, the MEA joining step includes the following steps (FIG. 4A and FIG. 4B). As shown in FIG. 4A, in the MEA joining step, a step of disposing the electrolyte membrane 18, the anode 20, the cathode 22, and the first frame shaped sheet 24 a is performed, in a manner that the inner peripheral portion 24 an of the first frame shaped sheet 24 a is disposed between the outer peripheral portion 20 c of the anode 20 and the outer peripheral portion 22 c of the cathode 22 and that the adhesive layer 24 c provided on at least the inner peripheral portion 24 an of the first frame shaped sheet 24 a is overlapped with the electrolyte membrane 18.

Further, in the MEA joining step, as shown in FIG. 4B, a step of thermal compression bonding to join the electrolyte membrane 18, the anode 20, the cathode 22, and the first frame shaped sheet 24 a by thermal compression bonding is performed, in a manner that the outer peripheral portion 18 c of the electrolyte membrane 18 is stacked on the outer peripheral portion 22 c of the cathode 22, and joined to the inner peripheral portion 24 an of the first frame shaped sheet 24 a through the adhesive layer 24 c.

In the thermal compression bonding step, a part of the adhesive layer 24 c (adhesive 24 d) is allowed to flow from a position between the first frame shaped sheet 24 a and the electrolyte membrane 18 to an area R surrounded by the inner peripheral end 24 ae of the first frame shaped sheet 24 a, the anode 20, and the electrolyte membrane 18. That is, the adhesive 24 d between the first frame shaped sheet 24 a and the electrolyte membrane 18 is softened (or liquefied) by heat, and pushed into the area R by the pressure (load) applied by a hot pressing apparatus. After the heat compression bonding step, the adhesive 24 d which flowed into the area R is hardened (solidified), and forms the adhesive layer 24 c (filling part 24 cf) fixed to the electrolyte membrane 18 in the area R. As a result, an adhesive layer 23 c is filled in the area R. The filling part 24 cf is continuous with (connected to) the adhesive layer 24 c between the first frame shaped sheet 24 a and the electrolyte membrane 18.

In this case, as shown in FIG. 2, in the frame equipped MEA 10 and the power generation cell 12 according to the embodiment of the present invention, the adhesive layer 24 c which joins the inner peripheral portion 24 an of the first frame shaped sheet 24 a and the outer peripheral portion 18 c of the electrolyte membrane 18 is filled in the area R surrounded by the inner peripheral end 24 ae of the first frame shaped sheet 24 a, the anode 20, and the electrolyte membrane 18. In the structure, it is possible to prevent exposure of the electrolyte membrane 18 in the area R. Accordingly, even if the electrolyte membrane 18 is expanded or contracted when the electrolyte membrane 18 is humidified or dried, it is possible to reduce the damage of the electrolyte membrane 18.

The thickness of the electrolyte membrane 18 and the thickness of the adhesive layer 24 c are smaller than the thickness of the first frame shaped sheet 24 a. By determining the thickness balance suitably in this manner, it is possible to fill the area R suitably without using the excessive quantity of the adhesive 24 d.

The present invention is not limited to the above described embodiment. Various modifications can be made without departing from the gist of the present invention.

The above embodiment is summarized as follows:

The above embodiment discloses the frame equipped membrane electrode assembly (10). The frame equipped membrane electrode assembly (10) includes the membrane electrode assembly (10 a) and the frame member (24), the membrane electrode assembly (10 a) including the electrolyte membrane (18), the first electrode (20) provided on one surface of the electrolyte membrane, and the second electrode (22) provided on the other surface of the electrolyte membrane, and the frame member including the resin sheet (24 a) provided on the outer peripheral portion of the membrane electrode assembly over its entire periphery, wherein the outer peripheral portion of the electrolyte membrane is disposed between the second electrode and the resin sheet, stacked on the outer peripheral portion of the second electrode, and joined to the inner peripheral portion of the resin sheet through the adhesive layer (24 c), and the adhesive layer is filled in the area (R) surrounded by an inner peripheral end of the resin sheet, the first electrode, and the electrolyte membrane.

The frame member may include another resin sheet (24 b) joined, through the adhesive layer, to a portion of the resin sheet protruding outside of the second electrode.

The step may be provided in the first electrode at the position corresponding to an inner peripheral end of the resin sheet.

The inner peripheral portion of the other resin sheet may have the overlap part (24 bk) overlapped with the outer peripheral portion of the first electrode, as viewed in a thickness direction of the membrane electrode assembly.

The thickness of the electrolyte membrane and the thickness of the adhesive layer may be smaller than the thickness of the resin sheet.

Further, the above embodiment discloses the fuel cell (12). The fuel cell includes the frame equipped membrane electrode assembly (10) and separators (14, 16) provided on both sides of the frame equipped membrane electrode assembly, respectively, the frame equipped membrane electrode assembly including the membrane electrode assembly (10 a) and the frame member (24), the membrane electrode assembly including the electrolyte membrane (18), the first electrode (20) provided on one surface of the electrolyte membrane, and the second electrode (22) provided on the other surface of the electrolyte membrane, and the frame member including the resin sheet (24 a) provided on the outer peripheral portion of the membrane electrode assembly over its entire periphery, wherein the outer peripheral portion of the electrolyte membrane is disposed between the second electrode and the resin sheet, stacked on the outer peripheral portion of the second electrode, and joined to the inner peripheral portion of the resin sheet through the adhesive layer (24 c), and the adhesive layer is filled in the area (R) surrounded by the inner peripheral end of the resin sheet, the first electrode, and the electrolyte membrane.

Further, the above embodiment discloses the method of producing the frame equipped membrane electrode assembly (10). The frame equipped membrane electrode assembly includes the membrane electrode assembly (10 a) and the frame member (24), the membrane electrode assembly including the electrolyte membrane (18), the first electrode (20) provided on one surface of the electrolyte membrane, and the second electrode (22) provided on the other surface of the electrolyte membrane, and the frame member (24) including the resin sheet (24 a) provided on the outer peripheral portion of the membrane electrode assembly over its entire periphery. The method includes the steps of disposing the electrolyte membrane, the first electrode, the second electrode, and the resin sheet in a manner that the inner peripheral portion of the resin sheet is disposed between the outer peripheral portion of the first electrode and the outer peripheral portion of the second electrode and that the adhesive layer (24 c) provided on at least the inner peripheral portion of the resin sheet is overlapped with the electrolyte membrane, and thermal compression bonding to join the electrolyte membrane, the first electrode, the second electrode, and the resin sheet by thermal compression bonding in a manner that the outer peripheral portion of the electrolyte membrane is stacked on the outer peripheral portion of the second electrode, and joined to the inner peripheral portion of the resin sheet through the adhesive layer, wherein, in the thermal compression bonding step, a part of the adhesive layer is allowed to flow from a position between the resin sheet and the electrolyte membrane to an area (R) surrounded by the inner peripheral end of the resin sheet, the first electrode, and the electrolyte membrane and to be filled in the area. 

What is claimed is:
 1. A frame equipped membrane electrode assembly comprising: a membrane electrode assembly comprising an electrolyte membrane, a first electrode provided on one surface of the electrolyte membrane, and a second electrode provided on another surface of the electrolyte membrane in a stacking direction; and a frame member including a first resin sheet and a second resin sheet attached to the first resin sheet by an adhesive layer disposed therebetween, the frame member provided on an outer peripheral portion of the membrane electrode assembly over its entire periphery, wherein: an inner end of the second resin sheet is spaced outwardly away from an inner end of the first resin sheet and from an outer edge portion of the second electrode, such that a gap is provided between the inner end of the second resin sheet and the an outer edge portion of the second electrode in a direction perpendicular to the stacking direction; an outer peripheral portion of the electrolyte membrane is disposed between the second electrode and the first resin sheet in the stacking direction, stacked on an outer peripheral portion of the second electrode, and joined to an inner peripheral portion of the first resin sheet through the adhesive layer; and the adhesive layer has a first thickness in an area between the first and second resin sheets, and a second thickness in said gap, the second thickness being greater than the first thickness, and the adhesive layer is also filled in an area surrounded by an inner peripheral end of the first resin sheet, the first electrode, and the electrolyte membrane.
 2. The frame equipped membrane electrode assembly according to claim 1, wherein a step is provided in the first electrode at a position corresponding to an inner peripheral end of the first resin sheet.
 3. The frame equipped membrane electrode assembly according to claim 1, wherein an inner peripheral portion of the second resin sheet has an overlap part overlapped with an outer peripheral portion of the first electrode, as viewed in a thickness direction of the membrane electrode assembly.
 4. The frame equipped membrane electrode assembly according to claim 1, wherein a thickness of the electrolyte membrane and a thickness of the adhesive layer are smaller than a thickness of the first resin sheet.
 5. A fuel cell comprising a frame equipped membrane electrode assembly and separators provided on both sides of the frame equipped membrane electrode assembly, respectively, the frame equipped membrane electrode assembly comprising: a membrane electrode assembly comprising an electrolyte membrane, a first electrode provided on one surface of the electrolyte membrane, and a second electrode provided on another surface of the electrolyte membrane in a stacking direction; and a frame member including a first resin sheet and a second resin sheet attached to the first resin sheet by an adhesive layer disposed therebetween, the frame member provided on an outer peripheral portion of the membrane electrode assembly over its entire periphery, wherein; an inner end of the second resin sheet is spaced outwardly away from an inner end of the first resin sheet and from an outer edge portion of the second electrode, such that a gap is provided between the inner end of the second resin sheet and the an outer edge portion of the second electrode in a direction perpendicular to the stacking direction; an outer peripheral portion of the electrolyte membrane is disposed between the second electrode and the first resin sheet in the stacking direction, stacked on an outer peripheral portion of the second electrode, and joined to an inner peripheral portion of the first resin sheet through the adhesive layer; and the adhesive layer has a first thickness in an area between the first and second resin sheets, and a second thickness in said gap, the second thickness being greater than the first thickness, and the adhesive layer is filled in an area surrounded by an inner peripheral end of the first resin sheet, the first electrode, and the electrolyte membrane.
 6. The frame equipped membrane electrode assembly according to claim 1, wherein the inner peripheral end of the second resin sheet is positioned inside the outer peripheral end of the first electrode over the entire periphery of the frame member.
 7. A frame equipped membrane electrode assembly comprising: a membrane electrode assembly comprising an electrolyte membrane, a first electrode provided on one surface of the electrolyte membrane, and a second electrode provided on another surface of the electrolyte membrane in a stacking direction; and a frame member including a first resin sheet and a second resin sheet attached to the first resin sheet by an adhesive layer disposed therebetween, the frame member provided on an outer peripheral portion of the membrane electrode assembly over its entire periphery, wherein: the inner peripheral end of the second resin sheet is positioned inside the outer peripheral end of the first electrode over the entire periphery of the frame member, an outer peripheral portion of the electrolyte membrane is disposed between the second electrode and the first resin sheet in the stacking direction, stacked on an outer peripheral portion of the second electrode, and joined to an inner peripheral portion of the first resin sheet through the adhesive layer; and the adhesive layer is also filled in an area surrounded by an inner peripheral end of the first resin sheet, the first electrode, and the electrolyte membrane. 